Hybrid Machining Processes

Most of the unconventional or advanced machining processes (AMPs) were developed after the World War II in response to the challenges of machining and/or finishing unusual shapes and/or sizes in the advanced and difficult-to-machine (DTM) materials or for those applications where use of conventional machining processes is technically unfeasible, detrimental to the useful material properties, uneconomical and unproductive. But, further development of advanced materials and emphasis on miniaturization and ultra-precision machining and/or finishing requirements exposed limitations of individual AMPs. These challenges are being met with the development of hybrid machining processes (HMPs) by either combining two AMPs or one AMP with a conventional machining process to exploit their capabilities in a single process and simultaneously overcome their individual limitations. This chapter introduces AMPs, defines and classifies HMPs and refers to their applications.

This chapter introduces electrochemical HMPs developed by combining electrochemical machining (ECM) with conventional finishing processes such as grinding, mechanical honing, buffing, deburring and superfinishing with an objective to overcome their limitations and to enhance their finishing capabilities. Electrochemical HMPs are generally recognized as micro-finishing processes which are used to finish gears, cylinders, micro-shafts, and other micro-, meso- and macro-engineered components in order to improve surface finish and/or to correct micro-irregularities. The current chapter also presents brief details of electrochemical-type advanced drilling processes which have been developed to meet specialized drilling requirements.

This chapter describes thermal-type HMPs in which EDM as the primary process of material removal is combined with either a conventional machining/finishing process or with an electrolytic dissolution-based process for improved machining/finishing characteristics and workpiece surface integrity. This hybridization enables thermal HMPs to reduce processing times by 2 to 3 times when compared to their constituent processes while producing surface finishes up to 0.1 µm. Some of the important applications of thermal HMPs are as follows: drilling of micro-holes and the production of slits in quartz and glass, machining of metal matrix composites and ceramics, and dressing of grinding wheels.

The growing trend of miniaturization of products and rapid development in precision engineering demand higher machining quality of micro-holes, micro-grooves and complicated 3D micro-structures in parts of especially difficult-to-machine materials. Assisted-type HMPs were developed specifically to overcome the limitations of advanced machining processes and to improve the machining quality and productivity. Assisted-type HMPs are another important category of HMPs whereby assistance of an external source is used to overcome the limitations of the primary material removal process to facilitate efficient and effective machining. This chapter discusses working principles, process mechanisms and typical applications of some important vibration, heat, abrasive and magnetic field-assisted hybrid machining processes.